diff --git a/lambda.hs b/lambda.hs
index 2c893e6..2922b01 100644
--- a/lambda.hs
+++ b/lambda.hs
@@ -1,24 +1,45 @@
-
 import Data.List
 import Data.Maybe
 
 -- A symbol denoting a variable; consists of a textual name and some (or no) apostrophes to ensure uniqueness
-data Symbol = Symbol { symBase :: String -- lowercase a to z
-                     , symLen  :: Int    -- nonnegative
-                     }
+class (Eq s) => Symbol s where
+  -- Present symbols (not including symbol to change) -> symbol to change ->
+  --   simplest unique symbol
+  findName :: [s] -> s -> s
+
+-- Symbol that appends apostrophes to become unique
+data SymApostrophe = SymApostrophe { symApoBase :: String -- lowercase a to z
+                                   , symApoLen  :: Int    -- nonnegative
+                                   }
   deriving (Eq)
 
-instance Show Symbol where
-  show (Symbol s n) = s ++ (replicate n '\'')
+instance Show SymApostrophe where
+  show (SymApostrophe s n) = s ++ (replicate n '\'')
+
+instance Symbol SymApostrophe where
+  findName other (SymApostrophe base n) =
+    let sameBase = filter ((base ==) . symApoBase) other
+        lengths = map symApoLen sameBase
+        freeLengths = [0..] \\ (nub lengths)
+    in SymApostrophe base (head freeLengths) -- [0..] is infinite
+
+-- Symbol that changes to another letter in the alphabet to become unique
+data SymLetter = SymLetter {symLetBase :: String } -- lowercase a to z, aa to zz, ...
+  deriving (Eq)
+
+instance Show SymLetter where
+  show (SymLetter l) = l
+
+instance Symbol SymLetter where
+  findName other _ = 
+    let bases = map symLetBase other
+        freeBases = names \\ (nub bases)
+    in  SymLetter (head freeBases)
+      where letters = ['a'..'z']
+            namesN 0 = [""]
+            namesN n = [n ++ [l] | n <- namesN (n - 1), l <- letters]
+            names = concatMap namesN [1..]
 
--- Present symbols (not including symbol to change) -> symbol to change ->
---   unique symbol with same base and minimal amount of apostrophes
-findName :: [Symbol] -> Symbol -> Symbol
-findName other (Symbol base n) =
-  let sameBase = filter ((base ==) . symBase) other
-      lengths = map symLen sameBase
-      freeLengths = [0..] \\ (nub lengths)
-  in Symbol base (head freeLengths) -- [0..] is infinite
 
 -- An expression. Can be a mere symbol, a lambda application, or a lambda abstraction.
 data Expression s = ESymbol s
@@ -36,6 +57,9 @@ showTopLevel :: (Show s) => Expression s -> String
 showTopLevel e@(EExpr _ _) = tail . init . show $ e
 showTopLevel e = show e
 
+printTopLevel :: (Show s) => Expression s -> IO ()
+printTopLevel = putStrLn . showTopLevel
+
 {-
 Apply a function
 Insert an expression into another expression:
@@ -43,7 +67,7 @@ Insert an expression into another expression:
   change all symbols within that expression to be unique in the expression's new context
   simplify all symbols
 -}
-simplifyExpr :: [(Symbol, Symbol)] -> [Symbol] -> Expression Symbol -> Expression Symbol
+simplifyExpr :: (Symbol s) => [(s, s)] -> [s] -> Expression s -> Expression s
 simplifyExpr mapping context (ESymbol s) = ESymbol $ fromMaybe (findName context s) $ lookup s mapping
 simplifyExpr mapping context (EExpr a b) = EExpr (simplifyExpr mapping context a) (simplifyExpr mapping context b)
 simplifyExpr mapping context (ELambda l e) =
@@ -52,135 +76,100 @@ simplifyExpr mapping context (ELambda l e) =
       newcontext = newl : context
   in  ELambda newl (simplifyExpr newmapping newcontext e)
 
-makeUnique :: [Symbol] -> Expression Symbol -> Expression Symbol
+makeUnique :: (Symbol s) => [s] -> Expression s -> Expression s
 makeUnique = simplifyExpr []
 
-simplify :: Expression Symbol -> Expression Symbol
+simplify :: (Symbol s) => Expression s -> Expression s
 simplify = makeUnique []
 
-insertExpr :: Symbol -> Expression Symbol -> [Symbol] -> Expression Symbol -> Expression Symbol
+insertExpr :: (Symbol s) => s -> Expression s -> [s] -> Expression s -> Expression s
 insertExpr r new context old@(ESymbol s)
   | r == s    = makeUnique context new
   | otherwise = old
 insertExpr r new context (EExpr a b) = EExpr (insertExpr r new context a) (insertExpr r new context b)
 insertExpr r new context (ELambda l e) = ELambda l (insertExpr r new (l : context) e)
 
-apply :: Expression Symbol -> Expression Symbol
+apply :: (Symbol s) => Expression s -> Expression s
 apply (EExpr (ELambda s l) b) = insertExpr s b [] l -- [], not [s]
 apply (EExpr a@(EExpr _ _) b) = EExpr (apply a) b
 apply e = e
 
+step :: (Symbol s) => Expression s -> Expression s
 step = simplify . apply
 
--- EXPERIMENT ZONE START --
-letters = ['a'..'z']
-namesN :: Int -> [String]
-namesN 0 = [""]
-namesN n = [n ++ [l] | n <- namesN (n-1), l <- letters]
-names :: [String]
-names = concatMap namesN [1..]
-findNewName :: [Symbol] -> Symbol
-findNewName other =
-  let bases = map symBase other
-      freeBases = names \\ (nub bases)
-  in  Symbol (head freeBases) 0
-simplifyExpr_ :: [(Symbol, Symbol)] -> [Symbol] -> Expression Symbol -> Expression Symbol
-simplifyExpr_ mapping context (ESymbol s) = ESymbol $ fromMaybe (findNewName context) $ lookup s mapping
-simplifyExpr_ mapping context (EExpr a b) = EExpr (simplifyExpr_ mapping context a) (simplifyExpr_ mapping context b)
-simplifyExpr_ mapping context (ELambda l e) =
-  let newl = findNewName context
-      newmapping = (l, newl) : mapping
-      newcontext = newl : context
-  in  ELambda newl (simplifyExpr_ newmapping newcontext e)
-makeUnique_ :: [Symbol] -> Expression Symbol -> Expression Symbol
-makeUnique_ = simplifyExpr_ []
-simplify_ :: Expression Symbol -> Expression Symbol
-simplify_ = makeUnique_ []
-insertExpr_ :: Symbol -> Expression Symbol -> [Symbol] -> Expression Symbol -> Expression Symbol
-insertExpr_ r new context old@(ESymbol s)
-  | r == s    = makeUnique_ context new
-  | otherwise = old
-insertExpr_ r new context (EExpr a b) = EExpr (insertExpr_ r new context a) (insertExpr_ r new context b)
-insertExpr_ r new context (ELambda l e) = ELambda l (insertExpr_ r new (l : context) e)
-apply_ :: Expression Symbol -> Expression Symbol
-apply_ (EExpr (ELambda s l) b) = insertExpr_ s b [] l -- [], not [s]
-apply_ (EExpr a@(EExpr _ _) b) = EExpr (apply_ a) b
-apply_ e = e
-step_ = simplify_ . apply_
--- EXPERIMENT ZONE END --
-
-_s :: String -> Expression Symbol
-_s s = ESymbol $ _ss s
-
-_ss :: String -> Symbol
-_ss s = Symbol s 0
+_sa = flip SymApostrophe 0
+_sl = SymLetter
+_ea s = ESymbol $ _sa s
+_el s = ESymbol $ _sl s
 
 main = do
   putStrLn "Testing: Showing expressions"
-  print (EExpr (_s "a") (EExpr (_s "b") (_s "c")))
-  print (EExpr (_s "a") (EExpr (_s "b") (EExpr (_s "c") (_s "d"))))
-  print (EExpr (EExpr (_s "a") (_s "b")) (_s "c"))
-  print (EExpr (EExpr (EExpr (_s "a") (_s "b")) (_s "c")) (_s "d"))
-  print (EExpr (EExpr (_s "a") (EExpr (_s "b") (_s "c"))) (_s "d"))
-  print (ELambda (Symbol "a" 0) (_s "a"))
-  print (ELambda (Symbol "a" 0) (EExpr (EExpr (_s "a") (EExpr (_s "b") (_s "c"))) (_s "d")))
+  print (EExpr (_ea "a") (EExpr (_ea "b") (_ea "c")))
+  print (EExpr (_ea "a") (EExpr (_ea "b") (EExpr (_ea "c") (_ea "d"))))
+  print (EExpr (EExpr (_ea "a") (_ea "b")) (_ea "c"))
+  print (EExpr (EExpr (EExpr (_ea "a") (_ea "b")) (_ea "c")) (_ea "d"))
+  print (EExpr (EExpr (_ea "a") (EExpr (_ea "b") (_ea "c"))) (_ea "d"))
+  print (ELambda (_sa "a") (_ea "a"))
+  print (ELambda (_sa "a") (EExpr (EExpr (_ea "a") (EExpr (_ea "b") (_ea "c"))) (_ea "d")))
   putStrLn ""
   
   -- test of findName (seems to be working) ~G
   putStrLn "Testing: Finding new symbols"
-  print $ findName [(Symbol "a" 0), (Symbol "b" 0), (Symbol "a" 1)] (Symbol "a" 4)
-  print $ findName [(Symbol "a" 0), (Symbol "b" 0), (Symbol "a" 1)] (Symbol "b" 3)
-  print $ findName [(Symbol "a" 0), (Symbol "b" 0), (Symbol "a" 1)] (Symbol "c" 2)
-  print $ findName [(Symbol "a" 1), (Symbol "a" 3), (Symbol "a" 0)] (Symbol "a" 1)
--- EXPERIMENT ZONE START --
-  print $ findNewName [(Symbol "a" 0), (Symbol "b" 0), (Symbol "a" 1)]
-  print $ findNewName [(Symbol "a" 0), (Symbol "b" 0), (Symbol "a" 1)]
-  print $ findNewName [(Symbol "a" 0), (Symbol "b" 0), (Symbol "a" 1)]
-  print $ findNewName [(Symbol "a" 1), (Symbol "a" 3), (Symbol "a" 0)]
--- EXPERIMENT ZONE END --
+  putStrLn "SymApostrophe"
+  print $ findName [(SymApostrophe "a" 0), (SymApostrophe "b" 0), (SymApostrophe "a" 1)] (SymApostrophe "a" 4)
+  print $ findName [(SymApostrophe "a" 0), (SymApostrophe "b" 0), (SymApostrophe "a" 1)] (SymApostrophe "b" 3)
+  print $ findName [(SymApostrophe "a" 0), (SymApostrophe "b" 0), (SymApostrophe "a" 1)] (SymApostrophe "c" 2)
+  print $ findName [(SymApostrophe "a" 1), (SymApostrophe "a" 3), (SymApostrophe "a" 0)] (SymApostrophe "a" 1)
+  putStrLn "SymLetter"
+  print $ findName [(_sl "a"), (_sl "b"), (_sl "a")] (_sl "a")
+  print $ findName [(_sl "a"), (_sl "b"), (_sl "d")] (_sl "b")
+  print $ findName [(_sl "a"), (_sl "d"), (_sl "c")] (_sl "c")
+  print $ findName [(_sl "b"), (_sl "a"), (_sl "c")] (_sl "d")
   putStrLn ""
   
   putStrLn "Testing: Applying expressions"
-  let t = (ELambda (_ss "a") (ELambda (_ss "b") (ESymbol (_ss "a"))))
-      f = (ELambda (_ss "a") (ELambda (_ss "b") (ESymbol (_ss "b"))))
-      n = (ELambda (_ss "a") (EExpr (EExpr (ESymbol (_ss "a")) (makeUnique [(_ss "a")] f)) (makeUnique [(_ss "a")] t)))
--- EXPERIMENT ZONE START --
-      n_ = (ELambda (_ss "a") (EExpr (EExpr (ESymbol (_ss "a")) (makeUnique_ [(_ss "a")] f)) (makeUnique_ [(_ss "a")] t)))
--- EXPERIMENT ZONE END --
-  print t
-  print f
-  print n
-  print $ simplify $ (ELambda (Symbol "a" 1) (ESymbol (Symbol "a" 1)))
-  print (EExpr n f)
-  putStrLn $ showTopLevel (EExpr n f)
+  let ta = (ELambda (_sa "a") (ELambda (_sa "b") (_ea "a")))
+      fa = (ELambda (_sa "a") (ELambda (_sa "b") (_ea "b")))
+      na = (ELambda (_sa "a") (EExpr (EExpr (_ea "a") (makeUnique [(_sa "a")] fa)) (makeUnique [(_sa "a")] ta)))
+      tl = (ELambda (_sl "a") (ELambda (_sl "b") (_el "a")))
+      fl = (ELambda (_sl "a") (ELambda (_sl "b") (_el "b")))
+      nl = (ELambda (_sl "a") (EExpr (EExpr (_el "a") (makeUnique [(_sl "a")] fl)) (makeUnique [(_sl "a")] tl)))
+  print ta
+  print fa
+  print na
+  print tl
+  print fl
+  print nl
+  print $ simplify $ (ELambda (SymApostrophe "a" 1) (ESymbol (SymApostrophe "a" 1)))
+  print $ simplify $ (ELambda (_sl "b") (ESymbol (_sl "b")))
+  putStrLn $ showTopLevel (EExpr na fa)
+  putStrLn $ showTopLevel (EExpr nl fl)
   putStrLn ""
   
   putStrLn "Replacing symbols: apostrophe"
   putStrLn "Running: not false"
-  print (EExpr n f)
-  print . step $ (EExpr n f)
-  print . step . step $ (EExpr n f)
-  print . step . step . step $ (EExpr n f)
+  printTopLevel (EExpr na fa)
+  printTopLevel . step $ (EExpr na fa)
+  printTopLevel . step . step $ (EExpr na fa)
+  printTopLevel . step . step . step $ (EExpr na fa)
   
   putStrLn "Running: not true"
-  print (EExpr n t)
-  print . step $ (EExpr n t)
-  print . step . step $ (EExpr n t)
-  print . step . step . step $ (EExpr n t)
+  printTopLevel (EExpr na ta)
+  printTopLevel . step $ (EExpr na ta)
+  printTopLevel . step . step $ (EExpr na ta)
+  printTopLevel . step . step . step $ (EExpr na ta)
   putStrLn ""
   
--- EXPERIMENT ZONE START --
-  putStrLn "Replacing symbols: new base"
+  putStrLn "Replacing symbols: letter"
   putStrLn "Running: not false"
-  print (EExpr n_ f)
-  print . step_ $ (EExpr n_ f)
-  print . step_ . step_ $ (EExpr n_ f)
-  print . step_ . step_ . step_ $ (EExpr n_ f)
+  printTopLevel (EExpr nl fl)
+  printTopLevel . step $ (EExpr nl fl)
+  printTopLevel . step . step $ (EExpr nl fl)
+  printTopLevel . step . step . step $ (EExpr nl fl)
   
   putStrLn "Running: not true"
-  print (EExpr n_ t)
-  print . step_ $ (EExpr n_ t)
-  print . step_ . step_ $ (EExpr n_ t)
-  print . step_ . step_ . step_ $ (EExpr n_ t)
+  printTopLevel (EExpr nl tl)
+  printTopLevel . step $ (EExpr nl tl)
+  printTopLevel . step . step $ (EExpr nl tl)
+  printTopLevel . step . step . step $ (EExpr nl tl)
   putStrLn ""
--- EXPERIMENT ZONE END --